U.S. Pat. No. 2,791,036 to Gericke entitled Liquid Level discloses a spirit level 10 having a leveling surface 11 for placing on a surface to be leveled, a top surface opposite the leveling surface, and a pair of opposite major surfaces extending between the leveling surface and the top surface. The spirit level 10 is provided with a liquid level tube 21 having right angularly extending portions 22 and 23 is formed with level indicating lines 24 and filled with a liquid 25 (see US '036 Col. 2, lines 13-15). Air forming a bubble 27 is trapped in the tube 21 and is adapted to cooperate with the indicator lines 24 in either arm 22 or 23 depending on the position of the level 10 (see US '036 Col. 2, lines 17-20). The spirit level 10 is provided with a retainer plate 38 which is highly polished and serves as a mirror to reflect an image of the arm 22 of the tube 21 as illustrated in FIG. 1 to permit the horizontal bubble vial therein to be viewed from eye level (see US '036 Col. 2, lines 39-42). A user can view the reflected image of the vial along a so-called direct opposite line of sight directly opposite the spirit level and within a limited so-called direct opposite angular viewing range in the order of ±5° with respect thereto. Any greater movement to the right or left prevents the user viewing the reflected image which limits his ability to work efficiently and comfortably.
Commonly owned U.S. Pat. No. 6,748,666 to Zugel et al. entitled Spirit Level discloses a spirit level 10 having a body 12 with a level face 14 for setting a surface to be leveled, a top surface opposite the leveling surface, and a pair of opposite major surfaces extending between the leveling surface and the top surface. The spirit level 10 includes one or more bubble vials 20 mounted in body 12 for setting a vertical surface and a bubble vial 22 for setting a horizontal surface. The spirit level 10 includes a reflective surface 36 mounted inside a hollow portion of body 12 at an angle to bubble vial 20 and to a viewing plane 32 which reflects the image of bubble vial 20 to the viewing plane. Reflective surface 36 can be a polished mirror or a prism. The spirit level also has a limited direct opposite angular viewing range in the order of ±5° with respect a direct opposite line of sight similar to Gericke.
Commonly owned U.S. Pat. No. 7,117608 to Zugel et al. entitled Spirit
Level which is a continuation of aforementioned U.S. Pat. No. 6,748,666 discloses spirit levels with arrangements for deploying a reflective surface external to a main body for reflecting an image of a vial for setting a vertical surface. However, such arrangements are vulnerable and can only be used from a single side of a spirit level.
There is a need for an improved spirit level so that a user can view a vial for setting a vertical surface over a wider viewing angle compared to the hitherto described spirit levels.